During Release 12, the LTE standard has been extended with support of device to device (D2D) (specified as “sidelink”) features targeting both commercial and Public Safety applications. Some applications enabled by Rel-12 LTE are device discovery, where devices are able to sense the proximity of another device and associated application by broadcasting and detecting discovery messages that carry device and application identities. The applications can exchange information through direct communications based on physical channels terminated directly between the devices.
Vehicle-to-X (V2X) Communications
D2D communications may be extended to support Vehicle-to-X (V2X) communication, which includes any combination of direct communication between vehicles, pedestrian carried devices, and infrastructure mounted devices. V2x communication may take advantage of available network (NW) infrastructure, although at least basic V2x connectivity can be possible in case of lack of available network infrastructure. Providing an LTE-based V2x interface may be economically advantageous because of the LTE economies of scale and it may enable tighter integration between communications with the NW infrastructure (vehicle-to-infrastructure (V2I)), (vehicle-to-pedestrian (V2P)), and (vehicle-to-vehicle (V2V)) communications, as compared to using a dedicated V2x technology.
V2x communications may carry both non-safety and safety information, where each of the applications and services may be associated with specific communication operational requirements sets, e.g., in terms of latency, reliability, capacity, etc.
The European Telecommunications Standards Institute (ETSI) has defined two types of messages for road safety: Co-operative Awareness Message (CAM) and Decentralized Environmental Notification Message (DENM).
A CAM message is intended to enable vehicles, including emergency vehicles, to notify their presence and other relevant parameters in a broadcast fashion. Such messages target other vehicles, pedestrians, and infrastructure, and are handled by their applications. A CAM message also serves as active assistance to safety driving for normal traffic. Devices check availability of a CAM message every 100 ms, yielding a maximum detection latency requirement of less than or equal to 100 ms for most CAM messages.
A DENM message is event-triggered, such as by braking, and the availability of a DENM message is also checked for every 100 ms.
Depending on the use case, latency requirements for CAM and DENM may vary significantly. As an example, latency may vary from 20 ms for pre-crash warnings to 100 ms for emergency stop or queue warnings, and may be up to 1000 ms for non-safety related use cases such as traffic flow optimization, curve speed warnings, etc.
The package size of CAM and DENM message can vary from more than 100 to more than 800 bytes, although the typical size is around 300 bytes depending on the specific V2X use case, message type (e.g. DENM can be larger than CAM), and depending on the security format included in the packet (e.g., full certificate or certificate digest). The message is supposed to be detected by all vehicles in proximity.
The Society of the Automotive Engineers (SAE) has defined a Basic Safety Message (BSM) for DSRC with various defined messages sizes. Based on the importance and urgency of the messages, the BSMs are further classified into different priorities.
Each subframe in a sidelink communication incurs a fixed overhead in the first symbol for AGC training and in the last symbol for a guard band. Such overhead may affect link and system performance.
The approaches described in the Background section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in the Background section are not prior art to the inventive embodiments disclosed in this application and are not admitted to be prior art by inclusion in the Background section. Therefore, any description contained in the Background section may be moved to the Detailed Description section.